The present invention relates to a method for making thermally-conductive interface articles. A thermoplastic composition is used to make the articles. Particularly, the composition comprises a base thermoplastic elastomer matrix, thermally-conductive filler material, and temperature-activated phase change material. The thermally-conductive articles can be used as thermal interfaces to dissipate heat from heat-generating electronic devices.
Electronic devices such as semiconductors, microprocessors, resistors, and circuit boards generate a substantial amount of heat that must be removed in order for the device to function properly. The industry uses thermally-conductive compositions to dissipate heat from such electronic components. Conventional thermally-conductive compositions can be used in a variety of ways. For example, a thermally-conductive sheet or pad material can be used as an interface between the surface of the heat-generating device (for example, a memory chip on an electronic circuit board) and an adjacent heat-dissipating device (for example, heat sink or cold plate). Such conventional thermally-conductive materials are made frequently from compositions comprising a thermosetting silicone elastomer and thermally-conductive filler material.
For instance, Feinberg et al., U.S. Pat. No. 5,060,114 discloses a silicone pad for removing heat from a packaged electronic device. The silicone pad is made by adding thermally-conductive particles (for example, aluminum powder, nickel, aluminum oxide, iron oxide, beryllium oxide, or silver) to a mixture of silicone resins and curing agents. The mixture is poured into a mold and cured in a heated oven.
Toya, U.S. Pat. No. 5,021,494 discloses a thermally-conductive silicone material comprising: a) polyorganosiloxane; b) a polyorganohydrogensiloxane; and c) a catalyst selected from the group consisting of platinum and platinum compounds; d) heat-transfer filler particles (for example, metals, metal oxides, or ceramics); and e) an adhesion promoter which cures through addition reactions.
Peterson, U.S. Pat. No. 5,011,870 discloses thermally-conductive organosiloxane compositions comprising a polyorganosiloxane and a mixture of thermally-conductive fillers including finely divided aluminum nitride particles and particles of an additional thermally-conductive filler that is compatible with the polyorganosiloxane.
In other applications, thermal pastes or greases containing polysiloxane oils and thermally-conductive fillers are smeared onto the electrical and heat-sink components to form a thermally-conductive interface.
It is also known that thermally-conductive polytetrafluoroethylene (PTFE) articles can be made. Hanrahan, U.S. Pat. No. 5,945,217 discloses a thermally-conductive interface comprising a PTFE matrix, thermally-conductive particles, and a phase change material. The patent describes making a composition by first coagulating a slurry of boron nitride with an aqueous dispersion of PTFE to form a powder and then compounding the powder with a lubricant consisting of polyethylene glycol and isopropyl alcohol.
Although the foregoing compositions and materials can be somewhat effective as thermally-conductive interfaces for some heat-removal applications, there is a need for an improved thermally-conductive composition having the following properties: 1) the composition should be capable of being net-shape molded into a desired interface article (for example, a film, gasket, or pad) so that no further tooling is required to produce the final shape of the interface article; 2) the composition (shaped article) should be capable of providing a tightly conforming interface between the heat-generating and heat-dissipating devices; 3) the composition (shaped article) should have good overall thermal conductivity and low contact resistance at the surfaces of the heat-generating and heat-dissipating devices.
The present invention provides an improved thermoplastic, thermally-conductive composition having the foregoing properties among others. The composition can be used to make thermally-conductive articles for use as thermal interfaces. The invention also encompasses methods for making such thermally-conductive articles.